The present invention provides an improved process for preparation of active hexagonal mesoporous silica catalyst which comprises, preparing an aqueous mixture of a silica source, an organic solvent, an organic template and the cation containing species which is desired to substitute "si" isomorphously in the final product, under stirring conditions to obtain the hydrolyzed silica precursor by known method and further stirring to get homogeneous mixture, subjecting this homogenous mixture to a source of microwave radiation for a period ranging from 1 to 30 min, separating the solid from the reaction mixture by conventional methods, washing the solid thoroughly by an organic solvent, drying the solid at a temperature in the range 40 to 1200c, calcining the solid for a period ranging between 3 to 24 hours to obtain the said product, impregnating the calcined solid product using chloroplatinic acid as platinum source by conventional method .

Full Text

The present invention relates to an improved process for the preparation of mesoporous molecular sieves, more particularly it relates to a process for the preparation of hexagonal mesoporous silica catalyst.
These materials have hexagonal ordered arrangements of uniform mesopores whose dimensions may be in the range 15 to 100 A°. The properties of these molecular sieves can be modified by introducing inorganic/organic species in the pores of the mesoporous materials and this modification can be obtained by using the method presently being reported or by the methods reported in the literature. The various applications of such materials could be in the fields of catalysis and membranes.
The conventional method employed for synthesis of hexagonal mesoporous silica is mixing the silica precursor in organic solvent and water, with an organic compound in organic solvent which can act as templating agent/dispersing agent/structure guiding agent with efficient stirring for a fixed period of time as reported in the following literature. 1)US Patent No. 5,098,684 (1992) 2)Peter T Tanev , Malama Chlbose, Thomas J Pinnawala Nature, 368, 321-323 (1994) 3 ) Peter T Tenev et al. Materials Research Society Symposium Proced. 371 , 63-67 (1995) 4) Y M Seroguchi et al. J. Porous Materials 4, (2) , 129 - 134 (1997) 5) A . Monnier, G D Stucky et al.Science, 261 1299 - 1303 ( 1993). The ratios of water / silica, templating agent / silica, , are critical to obtain a good quality final product. This mixture is, then aged at a suitable period of time to obtain a mixture containing precipitated / gelled solid product. The solid is filtered, dried and characterized by X-ray diffraction (XRD). The solid is, later calcined, at a sufficient temperature, in the range 500 to 700 ° C. The final solid product thus obtained is
characterized by XRD for its structure, by BET for determining surface area, pore size distribution and pore volume etc. The solid is then impregnated with chemical species which makes it catalytically active.

The above process is modified by changing the various parameters namely l)Silica source 2)Templating agent 3) Solvent / medium of reaction 4) pH of reaction 5) Water to Silica ratio 6) Introducing various species in the reaction mixture which will give desired species in the pores of the material prepared 7) Stirring time 8) Ageing time etc. Drawbacks:
1. The final product is very sensitive to all the parameters.
2. Stirring time and ageing time which are quite considerable, thereby
increasing the time for the preparation thereof.
3. The energy inputs in stirring process are considerable, increasing the cost of
production.
The inventors of the present invention have observed that the use of microwave (MW) irradiation during the process for crystallization of the product considerably reduces the time of crystallization.
The main object of the present invention is to provide improved process of the preparation of hexagonal mesoporous silica catalyst.
Another object of the present invention is to introduce inorganic / organic species into the pores of mesoporous silica and/or appropriate ions are substituted in to the structure to modify their properties.
The principle on which the process of present invention is developed, is based on l)The formation of a mixture containing a silica source, water, organic solvent, organic chemical which can act as templating agent / dispersing agent / structure guiding agent. 2)Stirring the mixture as prepared in (1) to make it homogenous, if necessary 3) subjecting the homogenous mixture as formed through steps 1&2 to a source of MW radiation for a period in the range 1-30 min. 4)Separating the solid formed in the reaction by filtration 5) Washing the solid thoroughly by a suitable solvent to remove the templating agent /dispersing agent /

structure guiding agent. 6) Drying the solid by conventional methods at a temp, in the range 40-120 ° C. 7) Calcining the solid in the temperature range 400 - 700° C. 8)Characterizing of the solid product thus formed by XRD for structure determination, BET for surface area , pore size distribution and pore volume determination, SEM & TEM for morphological properties of solid. An example of typical X ray pattern is shown in fig. 1
Accordingly, the present invention provides an improved process for preparation of active hexagonal mesoporous silica catalyst which comprises, preparing an aqueous mixture of a silica source, an organic solvent, an organic template and the cation containing species which is desired to substitute "si" isomorphously in the final product, under stirring conditions to obtain the hydrolyzed silica precursor by known method and further stirring to get homogeneous mixture, subjecting this homogenous mixture to a source of microwave radiation for a period ranging from 1 to 30 min, separating the solid from the reaction mixture by conventional methods, washing the solid thoroughly by an organic solvent, drying the solid by conventional methods at a temperature in the range 40 to 1200c, calcining the solid at a temperature in the range 400 to 7000c for a period ranging between 3 to 24 hours to obtain the said product, impregnating the calcined solid product using chloroplatinic acid as platinum source by conventional method.
In an embodiment of the present invention silica sources may be chosen from tetraethyl orthosilicate (TEOS), tetramethyl orthosilicate (TMOS), sodium silicate.

Cation containing species used may be such as zirconium, cobalt, titanium, Fe.
In another embodiment, the organic material which can act as templating agent / dispersing agent/structure guiding agent is Dodecylamine, (DDA), Cetyltrimethylammoniumbromide, Cetytrimethylphosphomium, Cetylpiridinium, Octadecyltrimethylphosphomium , Dodecyltrimethylammonium, Benzyltri-methylammonium , Decyltrimethylammonium, Veristyltrimethylammonium, and Dimethyldidodecylammonium.
In yet other embodiment, the mole ratio of template to silica source may be in the range of 0.1 to 0.3
In yet another embodiment the mole ratio of water to silica may be in the range of 20 to 40.
In yet another embodiment the time of homogenising the mixture by stirring can be in the range 0 to 2 hours.
In yet another embodiment the MW radiation wavelength is 2450 MHz .
Hydrolysis of silica precursor may be effected by using hydrochlorolic acid.
In a feature of present invention the template can be removed from the solid reaction product by refluxing with appropriate organic solvent or by extracting with appropriate organic solvent with the help of sohxlet apparatus.
In yet another feature, the species which makes the product catalytically active may be introduced in the product in situ or by conventional impregnation methods.
The process of the present invention is illustrated by the examples given below which are illusrtative only and should not be construed to limit the scope of present invention in any manner.

Example I
A) 2 gms. of Dodecyl amine (DDA) was dissolved in 8 ml. of ethyl alcohol. 0.06 gm of Copper phthalocyanine was dissolved in the above mixture . The resulting mixture was added to a solution of Tetraethyl Ortho Silicate (TEOS) in 4ml. ethyl alcohol . The final mixture has DDA/Si = 0.27 and Si / Cu = 400. B) 0.08 ml cone. HC1 was diluted to 18 ml. of distilled water. C) HC1 was added dropwise to a continuously stirred mixture A. The stirring was continued for 30 minutes. The resulting mixture was then subjected to MW treatment for 1 minute. The final solid product was filtered and thouroughly washed with alcohol. Solid was dried at 100° C and then calcined at 550° C for 12 hrs. The yield obtained was 99% on the basis of Si weight. The product thus obtained was characterised by XRD, giving characteristic peak at 2.4 deg. in diffractogram (fig. 1). BET characterisation gave surface area of 800 m2 /gm.
Example II
A) 0.08 gms. of ZrOCl 2 , 8H2O was dissolved in 10 ml of distilled water . This solution was added to 8.32 gms. of TEOS and stirred for 10 minutes. Si / Zr ratio was found to be 100. B) 2 gms. of DDA was dissolved in 12 ml. of ethyl alcohol and added dropwise to mixture A.The stirring was continued for about 15 minutes. C) 0.08 ml. of concentrated HC1 was dissolved in 18 ml. of distilled water and this solution was added dropwise to mixture B and stirred vigorously for 30 to 40 minutes.The mixture was then subjected to MW treatment for one minute. The resulting solid product was filtered and thoroughly washed with alcohol. The solid product was dried at 100 °C and then calcined at 550°C for 12 hrs. The product thus obtained was characterised by XRD. BET characterisation gave surface area to be 989 m2/gm.

Example III
A) 1 gm. of DDA was dissolved in 12 ml of ethyl alcohol (ratio DDA / Si = 0.135). This solution was added dropwise to 8.32 gms. of TEOS and stirred for 15 minutes. B) 0.08 ml concentrated HC1 was diluted to 18 ml of distilled water. C) Mixture B was added dropwise to a continuously stirred mixture A. The stirring was continued for 30 minutes. The mixture was then subjected to MW treatment for 2 minutes. The resulting solid product was filtered and thoroughly washed with alcohol. The final solid product was dried at 100 °C and then calcined at 550°C for 12 hrs. The product thus obtained was characterised by XRD. BET characterisation gave surface to be 650 m2/gm. The resulting solid product was imprignated by Platinum by conventional method using chloroplatinic acid as Platinum source.
Example IV
A) 4 gms. of DDA was dissolved in 12 ml of ethyl alcohol. This solution was added to 8.32 gms of TEOS and stirred for 15 minutes, (ratio DDA / Si = 0.54 ). B) 0.08 ml concentrated HC1 was diluted to 18 ml of water. C) Mixture B was added dropwise to a continuously stirred mixture A. The stirring was continued for 30 minutes. The mixture was then subjected to MW treatment for 3 minutes. The resulting solid product was filtered and washed thoroughly with ethyl alcohol. The final product was dried at 100°C and then calcined at 550°C for 12 hrs. Silver was impregnated by conventional method..
The product thus obtained was charactersed by XRD, BET surface area and Xray energy dispersive analysis. Surface area was found to be 800 m2 /gm.
The calcined product was immersed in 0.2 M chloro platinic acid aqueous solution for 30 min.; filtered , dried and calcined at 500 ° C.

Example V
A) 8.32 gms, of TEOS was stirred with O.453 gms. of Titanium tetrabutoxide [Ti(OC4H9)4] and l0ml.of isopropanol for 15 minutes . B) 2 gms of DDA was dissolved in 12 ml of ethyl alcohol. This solution was added dropwise to the continuous stirred mixture A. stirring continued for 30 minutes after the addition of the solution. C) 0.08 ml concentrated HC1 was diluted to 18 ml of water . This solution was added dropwise to the continuous stirred mixture of B. Stirring continued for 30 minutes after the complete addition of the solution .This mixture was then subjected to MW treatment for 5 minutes. The resulting solid product was filtered and washed thoroughly with ethyl alcohol. The final product was dried at 100°C and then calcined at 550°C for 12 hrs.
The product thus obtained was charactersed by XRD, BET surface area and X-ray energy dispersive analysis. Surface area was found to be 800 m2/gm.
The calcined product was immersed in 0.2 M chloro platinic acid aqueous solution for 30 min.; filtered, dried and calcined at 500 ° C. The main advantages of the present invention are:
1) Synthesis time is considerably reduced as compared to conventional methods
of preparation of ordered mesoporous materials.
2) The energy requirement of the synthesis is less as compared to reported
methods.
3) The product has good reproducibility and uniformity.
4) Impregnation of active species into pores of structure can be done either by
conventional methods or in situ impregnation.

5) For the formation of hexagonal structure in HMS catalyst it is essential to oligomerise the product by removing water molecules from silica gel. The use of conventional energies for removal of water molecules will affect the template structure thereby altering the characteristics and structure of final catalyst. This drawback has been eliminated by the use of microwave irradiation which selectively removes water molecule without disturbing the micelle structure. Therefore the novelty of the invention lies in use of microwave irradiation rather than the aging process which is conventionally used for the crystallization of the product. The invention has added advantage of considerably educing the time of crystallization and forming the final product almost spontaneously instead of waiting for 12-24 hrs as in conventional method.

We Claim:
1. An improved process for preparation of active hexagonal mesoporous silica
catalyst which comprises, preparing an aqueous mixture of a silica source, an
organic solvent, an organic template and the cation containing species which is
desired to substitute "Si" isomorphously in the final product, under stirring
conditions to obtain the hydrolyzed silica precursor by known method and further
stirring to get homogeneous mixture, subjecting this homogenous mixture to a
source of microwave radiation for a period ranging from 1 to 30 min, separating
the solid from the reaction mixture by conventional methods, washing the solid
thoroughly by an organic solvent, drying the solid by conventional methods at a
temperature in the range 40 to 120°C, calcining the solid at a temperature in the
range 400 to 700°C for a period ranging between 3 to 24 hours to obtain the said
product , impregnating the calcined solid product using chloroplatinic acid as
platinum source by conventional method .
2. An improved process as claimed in claim 1, wherein silica sources may be
chosen from tetraethyl orthosilicate (TEOS), tetramethyl orthosilicate (TMOS),
sodium silicate.
3. An improved process as claimed in 1 and 2, wherein organic solvent is chosen
from ethyl alcohol, methyl alcohol and propyl alcohol.
4. An improved process as claimed in claims 1-3, wherein template is
dodecylamine(DDA)..
5. An improved process as claimed in claims 1-4, wherein the molar ratio of silica -
template is in the range of 2-3.
6. An improved process as claimed in claims 1-5, wherein the molar ratio of water -
silica is in the range of 20 - 40.
7. An improved process as claimed in claims 1-6, wherein microwave frequency is
about 2450 MHz.
8. An improved process as claimed in claims 1-7, wherein the microwave treatment
given may be for 1-30 minutes.

9. An improved process as claimed in claims 1 to 8, wherein the cation containing
species used is such as zirconium, cobalt, titanium, Fe.
10. An improved process as claimed in claims 1 to 9, wherein the hydrolysis of silica
precursor is effected by using hydrochloric acid.
11. An improved process for preparation of active hexagonal mesoporous silica
catalyst as fully described hereinbefore with references to examples contained
therein and drawing accompanying this specification.